TREATMENT OPTIMIZATION BY COMBINED A-EMITTER (ARPT)/RADIOTHERAPY (XRT) DOSIMETRY FOR PROSTATE CANCER PATIENTS We propose to demonstrate a cloud-based software service for Combination alpha-emitter radiopharmaceutical therapy (?RPT) and external-beam radiotherapy (XRT); (CX?RPT) treatment-planning. Both modalities deliver radiation. We will demonstrate feasibility clinically by collecting the data needed from an existing Hopkins trial evaluating combination XRT with Xofigo (223Ra-dichloride), an ?RPT that concentrates ?-particle radiation to prostate cancer bone metastases. By ?piggybacking? on this trial we will evaluate the dosimetry technology for CX?RPT that we propose to develop and commercialize without having to cover the costs of the entire trial. Objective 1: Via the studies proposed and data collected, demonstrate, retrospectively, that 30% of the patients would have benefitted from an adjustment in their XRT treatment plan to meet tumor dose criteria while respecting organ dose constraints. Objective 2: Implement the CX?RPT-enabling software (3D-RD-X) in a web/cloud system as a prototype for a future software service add-on to existing 3D-XRT treatment-planning systems. Objective 3: Validate 3D-RD-X against RPTDose, our Phase I proof-of-concept prototype. The work proposed will enable a treatment-planning-based combination treatment of XRT and ?RPT using cloud-based software. This will improve patient care by reducing the empiricism typical of chemo-XRT combination therapy and demonstrate the efficacy of a cloud-based system for performing the treatment planning.